In a group of 100 children, the mean weight of a child is 15 kg. The SD is 1.5 kg. Which one of the following is TRUE

Okay, let's tackle this question. The user provided a question about mean and standard deviation in a group of children's weights. The correct answer is missing, but I need to figure out the right approach.

First, the core concept here is understanding standard deviation in a normal distribution. Since the sample size is 100, which is large, we can assume the data is normally distributed. The mean is 15 kg, and the SD is 1.5 kg. In a normal distribution, about 68% of the data falls within one SD of the mean, 95% within two SDs, and 99.7% within three SDs.

So, the correct answer should relate to these percentages. For example, 68% of the children would have weights between 13.5 kg and 16.5 kg (15 ± 1.5). Similarly, 95% would be between 12 kg and 18 kg (15 ± 3). The options would likely test these ranges.

Now, the wrong options might include incorrect percentages or ranges. For instance, someone might confuse 68% with 95%, or miscalculate the SD intervals. Also, outliers or incorrect interpretation of SD could be distractors.

The clinical pearl here is remembering the 68-95-99.7 rule for normal distributions. It's high-yield for statistics questions in exams.

**Core Concept**
This question tests understanding of the **normal distribution** and **standard deviation (SD)** in statistical analysis. In a normally distributed sample, approximately 68% of data falls within ±1 SD from the mean, 95% within ±2 SD, and 99.7% within ±3 SD.

**Why the Correct Answer is Right**
Given a mean of 15 kg and SD of 1.5 kg:
- **68% of children** will have weights between **13.5 kg (15 - 1.5)** and **16.5 kg (15 + 1.5)**.
- **95%** will fall between **12 kg (15 - 3×1.5)** and **18 kg (15 + 3×1.5)**.
The correct answer must align with these statistical ranges, reflecting the proportion of data within specific SD intervals.

**Why Each Wrong Option is Incorrect**
- **Option A:** If suggesting 50% within ±1 SD, this ignores the 68% rule.
- **Option B:** If claiming 95% within ±1 SD, this misapplies the 68-95-99.7 distribution.
- **Option C:** If proposing 99.7% within ±2 SD, this incorrectly shifts the 3 SD range.
- **Option D:** If stating 68% within ±2 SD, this confuses SD intervals with their corresponding percentages.

**Clinical Pearl / High-Yield Fact**
Remember the **68-95-99.7 rule** (empirical rule) for normal distributions. For NEET PG and USMLE, always associate **±1 SD = 68%**, **±2 SD = 95%**, and

✓ Correct Answer: A. 95% of all children weigh between 12 and 18 kg